1. Field of the Invention
This invention relates to a magnetic recording medium, a method of manufacture therefor, and for an apparatus for magnetic recording and reproducing using this magnetic recording medium.
2. Description of the Related Art
So-called perpendicular magnetic recording media, in which the axis of easy magnetization within the magnetic film is arranged generally perpendicularly, have received a great deal of attention because the effect of the demagnetizing field at the bit boundaries is small even when high recording density has been realized, it is possible to achieve noise reduction due to the formation of magnetic recording domains which have distinct boundaries, and moreover, for having strong thermal fluctuation effects because it is possible to realize high recording density even if the comparative bit volume is large.
For example, in Japanese Patent Application, First Publication No. Hei 7-44852, a magnetic recording medium having a perpendicular magnetic film comprising a CoCrPtTa alloy and soft magnetic backlayer is disclosed.
In Japanese Patent Application, First Publication No. Hei 5-334644, a magnetic recording medium having a perpendicular magnetic film comprising an alloy in which V has been added to a CoCrTa alloy is disclosed.
In Japanese Patent Application, First Publication No. Hei 5-343225, a magnetic recording medium having a perpendicular magnetic film comprising an alloy in which B has been added to a CoCrTa alloy is disclosed.
In Japanese Patent Application, First Publication No. Hei 11-296833, a magnetic recording medium having a perpendicular magnetic film having a two-layered structure is disclosed.
For perpendicular magnetic recording media, in order to obtain magnetic characteristics such as coercive force and squareness ratio, it is important to increase the perpendicular orientation in the perpendicular magnetic film.
However, with conventional magnetic recording media, when the orientation of the perpendicular magnetic film becomes better, since the direction of the growth of the crystals becomes uniform, the distance between the magnetic grains becomes smaller, and noise due to the effect of the exchange coupling increases.
In consideration of the above circumstances, an object of the present invention is to provide a magnetic recording medium with which it is possible to obtain improved noise characteristics, a manufacturing method therefor, and a apparatus for magnetic recording and reproducing.
The magnetic recording medium of the present invention comprises on a non-magnetic substrate at least a soft magnetic undercoat film comprising a soft magnetic material, an orientation control film for controlling the orientation of the film directly above, a perpendicular magnetic film in which the axis of easy magnetization is oriented mainly perpendicularly with respect to the substrate, and a protection film. The perpendicular magnetic film has a structure in which a large number of magnetic grains are separated by a grain boundary layer, and the average separating distance between these magnetic grains along a straight line which connects the centers of gravity of neighboring magnetic grains is 1 nm or greater.
The average grain diameter is preferably 4 to 12 nm.
It is preferable for the magnetic recording medium of the present invention to have a nucleation field (xe2x80x94Hn) of 0 (Oe) or greater as measured using a vibrating sample magnetometer.
In the units of magnetic field strength, there is the conversion relationship of:
4xcfx80xc3x9710xe2x88x923 (Oe)=1(A/m)
The nucleation field is preferably a value measured at 70xc2x0 C.
It is preferable for the perpendicular magnetic film to comprise a CoCrPtX type alloy (where X is one or more of Mo, B, V, W, Zr, Re, Cu, Ru, Hf, Ir, and Y), and for the amount of X contained to be 0.5 to 15 at %.
In the present invention, it is possible to adopt a constitution in which X is B and the amount of X contained is 10 at % or less.
The perpendicular magnetic film may comprise Cr in an amount of 12 to 26 at %, Pt in an amount of 10 to 24 at %, X in an amount of 0.5 to 15 at %, and the remainder as Co.
The perpendicular magnetic film preferably comprises Co and Cr, and when the Cr concentration in the magnetic grains is c1, and the Cr concentration in the grain boundary layer is c2, c2/ c1 is 1.4 or greater.
The Cr concentration in the grain boundary layer is preferably 15 at % or greater.
The perpendicular magnetic film may have a granular structure.
A structure may be adopted in which a non-magnetic intermediate film is provided between the orientation control film and the perpendicular magnetic film, and the non-magnetic intermediate film comprises a CoCrPtX1 type alloy (X1 being at least one of Mo, Ta, B, V, W, Zr, Re, Cu, Ru, Hf, Ir, and Y), the content of Cr being 20 to 45 at %, the content of Pt being 5 to 25 at %, the content of X1 being 0.5 to 20 at %, and the remainder being Co.
It is preferable that the content of Cr is 30 to 45 at %.
The non-magnetic intermediate film preferably comprises Co and Cr, has a structure in which crystal grains having a high Cr content are separated by a grain boundary layer having a low Cr content, and the average separating distance between the crystal grains along straight lines which connect the centers of gravity of mutually neighboring crystal grains is 1 nm or greater.
The average grain diameter of the crystal grains is preferably 4 to 12 nm.
The manufacturing method for a magnetic recording medium of the present invention is a manufacturing method for a magnetic recording medium having on a non-magnetic substrate, at least a soft magnetic undercoat film comprising a soft magnetic material, an orientation control film for controlling an orientation of a film directly above, a perpendicular magnetic film in which the axis of easy magnetization is oriented mainly perpendicularly with respect to the substrate, and a protection film, wherein the perpendicular magnetic film has a structure in which a large number of magnetic grains are separated by a grain boundary layer, and the average separating distance between the magnetic grains along a straight line which connects centers of gravity of mutually neighboring magnetic grains is 1 nm or greater.
The apparatus for magnetic recording and reproducing of the present invention comprises a magnetic recording medium, and a magnetic head for recording and reproducing information on the magnetic recording medium, wherein the magnetic recording medium comprises on a non-magnetic substrate, at least a soft magnetic undercoat film comprising a soft magnetic material, an orientation control film for controlling an orientation of a film directly above, a perpendicular magnetic film in which an axis of easy magnetization is oriented mainly perpendicularly with respect to the substrate, and a protection film, and wherein the perpendicular magnetic film has a structure in which a large number of magnetic grains are separated by a grain boundary layer, and the average separating distance between the magnetic grains along a straight line which connects centers of gravity of mutually neighboring magnetic grains is 1 nm or greater.